Polymers and Physical Properties

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Objective

Students will be able to identify physical and chemical properties of substances in a reaction and provide evidence that mass is conserved in reactions.

Big Idea

Students explore physical and chemical properties of polymers as they make slime, experiment with insta-snow polymer, and stick a skewer through a balloon without it popping!

Introduction and Connection to the NGSS and Common Core

In this lesson, students obtain information from text as they work on using some text strategies called "Talking to the Text" and the "Ladder of Discourse".  Then, they complete a fun set of labs dealing with polymers including making "goo", using Insta-Snow, and sticking a skewer through a balloon.  Then, they utilize discussion strategies to have meaningful group discourse.

This lesson is designed to address the following NGSS and Common Core standards:

MS-PS1-1 Develop models to describe the atomic composition of simple molecules and extended structures.

MS-PS1-2  Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

MS-PS1-5  Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved. 

CCSS.ELA-LITERACY.WHST.6-8.1.B  Support claim(s) with logical reasoning and relevant, accurate data and evidence that demonstrate an understanding of the topic or text, using credible sources.

CCSS.ELA-LITERACY.RST.6-8.4  Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 6-8 texts and topics.

CCSS.ELA-LITERACY.RST.6-8.9   Compare and contrast the information gained from experiments, simulations, video, or multimedia sources with that gained from reading a text on the same topic.

CCSS.ELA-LITERACY.RST.6-8.10  By the end of grade 8, read and comprehend science/technical texts in the grades 6-8 text complexity band independently and proficiently.

Science and Engineering Practices:

When using the text strategies utilized in this lesson, students think deeply about text in order to make their own conclusions and consider solutions to problems.  Thus, students are using the Science and Engineering Practice of Generating Questions and Designing Solutions, which states that, "Students at any grade level should be able to ask questions of each other about the texts they read, the features of the phenomena they observe, and the conclusions they draw from their models or scientific investigations. For engineering, they should ask questions to define the problem to be solved and to elicit ideas that lead to the constraints and specifications for its solution." (SP1

In preparation for performing the lab stations, students use strategies to obtain scientific information and evidence from text (SP7).  In addition, students back up their explanations in the lab document with evidence from their qualitative observations (SP8).

Crosscutting Concepts:

When students discuss what they saw in the lab in comparison to what they read in the text, students can begin to see patterns in the structures  and properties of polymers.  Thus, students can begin to see that macroscopic patterns are related to the nature of microscopic and atomic-level structure (Patterns).  In addition, students explore how the properties of polymers relate to their structure (Structure and Function).

As a part of this lab, the students set up a mixture of Insta-snow and water and record the mass.  Weeks later, students return to their mixtures once the water is evaporated and measure the mass again in order to track the mass of the mixture and notice that matter is conserved in physical processes (Energy and Matter).

Connecting to the Essential Question: What are you going to learn today?

5 minutes

Ask students, "What are you going to learn today?".  Students should respond by saying that they will be answering the Essential Question, "How do particles combine into new stubstances? And, what evidence can show how the physical and chemical properties of the substances change?"  This EQ is posted on my board and on the student's Chemistry Unit Plan.  

Explain that today we are going to go through a series of lab stations that will ask them to look at the properties of a type of molecule called a polymer.  Specifically, students will focus on Skill 4 of their unit plan, "I can identify the physical and chemical properties of the reactants and products in a reaction."  (It is important to note that my students have already been introduced to physical and chemical properties before this lab.  The notes sheet along with some true/false statements relating these notes along with the answer key is included in the resources.)

Mini Lesson: Polymer Properties and The Ladder of Discourse

25 minutes

Provide students with the polymers reading that is included in the resource section.  Ask students to "Talk to the Text" and work their way up the "Ladder of Discourse" as they interact with the text.  Students document their thinking as they read in the margins of the text and try to reach real discourse as they interact with the text.

The levels of the "Ladder of Discourse" are "Tweets" (text to self connections), "Huh?'s"(questions or concepts they do not understand), "Found It" (finding answers to questions through context clues or finding science answers), and "Discourse" (combining ideas to think beyond the text).  

For more background on "talking to the text" and the "Ladder of Discourse" check out the following lessons.  These lessons include videos of me demonstrating these strategies and student work.

Talking to the Text:  Mystery Box Modeling:  Energy TransformationsHow does heat move?Thermal Protection Systems

Ladder of Discourse:  Crack that Marble LabRefracting TelescopesEngineering Earthquake Structures

In the student work below, notice that the student "talked to the text" to show their thought process as they read.  

Here are some specific examples of the students generating new ideas and design solutions from the ideas presented in the text.  The first student suggests that after reading about the properties of polymers, he could possibly design a cell phone case with a polymer (because they are flexible). This case could fit all kinds of phones and would eliminate the need for buying a separate case for each phone.  The other student states that they possibly could try to organize polymers by properties into a table like the Periodic Table, but organized by number of monomers in the chain as opposed to atomic number.

 

             

For an even closer look at some of the "Found It!'s" and "Discourse" that my students came up with watch the video below.  I think it will give you some great insight into how student thinking changed as a result of taking in new information using these text strategies.

 

Polymer Labs

45 minutes

Have students go through the series of lab stations.  I have included a Polymer Lab Student Document and Answer Key in the resource section.  However, I do not have the students write anything down.  The focus of this lab is on discourse amongst lab groups.  Thus, I just ask that students discuss these questions as they go through the stations.  After the lab, students go through a more rigorous discussion.

Station 1:  Who Ya Gonna Call?

  1. Pour a quarter cup of glue into a plastic cup.
  2. Add a quarter cup of water to the glue and stir thoroughly. 
  3. Add a few drops of food coloring.
  4. Pour a little of the borax solution into an empty cup and add a little at a time with your eyedropper to the glue-water mixture.  The slime will collect on your stick as you stir.
  5. You do not want to add too much borax!  A good rule of thumb is to stop adding borax when there is still a little fluid in the bottom of the cup.
  6. Play with the slime.  Try to bounce it, stretch it, and lay it on a piece of newspaper and peel it back.

Station 2:  The Amazing Balloon Trick

  1. Lubricate the end of the needle with Vaseline.
  2. Inflate a balloon to about half of its potential volume.  Tie off the balloon.
  3. Slowly stick the needle through the balloon and out the other end, near to where it is tied.  Amazing, it doesn’t pop!

Station 3:  Insta-Snow

  1. Add 20 mL of water to an empty beaker.
  2. Measure one teaspoon of sodium polyacrylate and add it to an empty beaker.
  3. Pour the 20 mL of water into the sodium polyacrylate.
  4. Play with it!  Touch it!
  5. Add 5 mL of water to the polymer until it turns to slush.
  6. Record observations on the table.
  7. Feel the slush as you add water.
  8. Now add salt to the mixture.
  9. Observe.

Watch how awesome it is when salt is added to the mixture!

Station 4:  Conservation of Mass

Post Instant Snow Lab:

  1. Label a small beaker with the names of the members in your group.
  2. Add one small scoop of sodium polyacrylate to a beaker and measure the mass.
  3. Measure the mass of the beaker with the sodium polyacrylate and record the mass in the data table.
  4. Place an different empty graduated cylinder on the scale.  Press the “Zero” button.  The scale should read 0.0 grams.
  5. Add 10 milliliters of water to the graduated cylinder.
  6. Record the mass of the water in the data table.
  7. Pour the water in the beaker of sodium polyacrylate.
  8. Measure the new mass of the sodium polyacrylate beaker.
  9. Place in the window sill. 
  10. After 1 week, measure the mass of the beaker again.

Initial Set Up With Water Added:

After Weeks/Post Evaporation:

This station is used to set up a reaction that will take place over a couple of weeks and will be referred to again when I teach the law of conservation of mass.  The mass of the original powder ends up being the same after weeks once the water has evaporated.

Polymer Discourse: Using Discussion Techniques

15 minutes

Explain to students that they are going to work in small groups to practice the discussion techniques they have been working on over the past lessons.  (In order for these discussions to be effective, I strongly encourage you to look at the Fishbowl Discussion Activity in the S'Mores, Discourse, and Properties Lesson.

Remind students to use as many of the sentence starters as they can, by referring to their "Fishbowl Activity" discussion document and to have their text handy.  Explain that you will be providing the students with a series of questions to answer; however, the conversation can be organic.  Let conversations flow and develop naturally.  These conversations do not need to go in the order of the discussion questions nor does each group need to stop and read each question word for word.  The idea is that students go through discourse  and deep thinking about the polymers, text, and lab stations.

Discussion Questions:

  • What makes a polymer a polymer?
  • Would the slime be considered a polymer?  Provide evidence!
  • Would the balloon be considered a polymer?  Provide evidence?
  • Describe the properties of Insta-Snow.
  • How is regular snow different from Insta-Snow?  How is it the same?
  • When salt was added, did the Insta-Snow melt?***

***This last question is very important to the next lesson, when I talk about phase changes. Adding the salt does not make the Insta-snow melt, it causes the polymer chain to break down and release the water.  Students will debate this one!  Some will explain that something can't melt without energy being added or removed and in this case neither happened.  Others will say, "Well, we add salt to the roads to melt the ice in the winter.  That's the same thing that happened here."  In the debrief of this question, it will be important that students see the difference between melting and what actually happened in this lab. 

The video of the group below is the prime example of how using sentence starters and practicing discourse is beneficial.  The students always have great ideas; however, previous to this day, their conversations tended to be one sided and filled with students interrupting each other or just trying to talk over each other.  In this discussion, notice how many of the sentence starters are used and every member of the group is brought into the conversation.  And, multiple students touch and refer to the text.  Moreover, the students ask questions of each other when they are confused and appropriately disagree with group members in a respectful way.  Another note:  You might sense a hint of "cheesiness".  When introducing sentence starters for discussion practice, students will read them with a corny voice.  However, even if read with a corny tone, the discussions improve! Embrace the cheese!

  

Students need to refer to both evidence from text and from the lab stations in order to have effective dialogue.  Notice how these students both reference scientific vocabulary, observations they saw from the balloon lab, and how the student at the end interjects with a text reference to make their claim that the balloon is a polymer even stronger.

One thing that starts happening when practicing discussion techniques is that leaders emerge.   And, the sentence starters give them the confidence to do it.  Some students worry about being "pushy"; however, now that students have these sentences in front of them that the other students know I told them to say, it removes some of that pressure.  

In the video below, the student begins with a text reference.  When referencing it, she asks her group members to turn to the page and follow along with her, bringing the whole group into the text.  

Closure

5 minutes

I close with the whole class by asking the lab groups to share what they discussed.  This is a great opportunity to check if student discussions are on the right track.  In addition, whole group discussions following small group discourse are great opportunities to get more students involved in group discussions.  Students feel as if they have had practice and gain confidence to share their ideas when they otherwise may not have.